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Clifford AM, Wilkie MP, Edwards SL, Tresguerres M, Goss GG. Dining on the dead in the deep: Active NH 4 + excretion via Na + /H + (NH 4 + ) exchange in the highly ammonia tolerant Pacific hagfish, Eptatretus stoutii. Acta Physiol (Oxf) 2022; 236:e13845. [PMID: 35620804 DOI: 10.1111/apha.13845] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 05/22/2022] [Accepted: 05/23/2022] [Indexed: 01/29/2023]
Abstract
AIM Pacific hagfish are exceptionally tolerant to high environmental ammonia (HEA). Here, we elucidated a cellular mechanism that enables hagfish to actively excrete ammonia against steep ammonia gradients expected to be found inside a decomposing whale carcass. METHODS Hagfish were exposed to varying concentrations of HEA in the presence or absence of environmental Na+ , while plasma ammonia levels were tracked. 14 C-methylammonium was used as a proxy for NH4 + to measure efflux in whole animals and in isolated gill pouches; the latter allowed us to assess the effects of amiloride specifically on Na+ /H+ exchangers (NHEs) in gill cells. Western blotting and immunohistochemistry were utilized to evaluate the abundance and sub-cellular localization of Rhesus glycoprotein (Rh) channels in the response to HEA. RESULTS Hagfish actively excreted NH4 + against steep inwardly directed ENH4 + (ΔENH4 + ~ 35 mV) and pNH3 (ΔpNH3 ~ 2000 μtorr) gradients. Active NH4 + excretion and plasma ammonia hypo-regulation were contingent on the presence of environmental Na+ , indicating a Na+ /NH4 + exchange mechanism. Active NH4 + excretion across isolated gill pouches was amiloride-sensitive. Exposure to HEA resulted in decreased abundance of Rh channels in the apical membrane of gill ionocytes. CONCLUSIONS During HEA exposure, hagfish can actively excrete ammonia against a steep concentration gradient using apical NHEs energized by Na+ -K+ -ATPase in gill ionocytes. Additionally, apical Rh channels are removed from the apical membrane, presumably to reduce ammonia loading from the environment. We suggest that this mechanism allows hagfish to maintain tolerable ammonia levels while feeding inside decomposing carrion, allowing them to exploit nutrient-rich food-falls.
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Affiliation(s)
- Alexander M Clifford
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, La Jolla, California, USA.,Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Bamfield Marine Sciences Centre, Bamfield, British Columbia, Canada
| | - Michael P Wilkie
- Department of Biology and Laurier Institute for Water Science, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - Susan L Edwards
- Department of Biological Sciences, Wright State University, Dayton, Ohio, USA
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California, La Jolla, California, USA
| | - Greg G Goss
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.,Bamfield Marine Sciences Centre, Bamfield, British Columbia, Canada
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Giacomin M, Drummond JM, Supuran CT, Goss GG. The roles of plasma accessible and cytosolic carbonic anhydrases in bicarbonate (HCO 3-) excretion in Pacific hagfish (Eptatretus stoutii). J Comp Physiol B 2022; 192:713-725. [PMID: 36098803 DOI: 10.1007/s00360-022-01459-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Revised: 08/08/2022] [Accepted: 08/23/2022] [Indexed: 11/29/2022]
Abstract
Pacific hagfish (Eptatretus stoutii) are marine scavengers and feed on decaying animal carrion by burrowing their bodies inside rotten carcasses where they are exposed to several threatening environmental stressors, including hypercapnia (high partial pressures of CO2). Hagfish possess a remarkable capacity to tolerate hypercapnia, and their ability to recover from acid-base disturbances is well known. To deal with the metabolic acidosis resulting from exposure to high CO2, hagfish can mount a rapid elevation of plasma HCO3- concentration (hypercarbia). Once PCO2 is restored, hagfish quickly excrete their HCO3- load, a process that likely involves the enzyme carbonic anhydrase (CA), which catalyzes HCO3- dehydration into CO2 at the hagfish gills. We aimed to characterize the role of branchial CA in CO2/HCO3- clearance from the plasma at the gills of E. stoutii, under control and high PCO2 (hypercapnic) exposure conditions. We assessed the relative contributions of plasma accessible versus intracellular (cytosolic) CA to gill HCO3- excretion by measuring in situ [14C]-HCO3- fluxes. To accomplish this, we employed a novel surgical technique of individual gill pouch arterial perfusion combined with perifusion of the gill afferent to efferent water ducts. [14C]-HCO3- efflux was measured at the gills of fish exposed to control, hypercapnic (48 h) and recovery from hypercapnia conditions (6 h), in the presence of two well-known pharmacological inhibitors of CA, the membrane impermeant C18 (targets membrane bound, plasma accessible CA) and membrane-permeant acetazolamide, which targets all forms of CA, including extracellular and intracellular cytosolic CAs. C18 did not affect HCO3- flux in control fish, whereas acetazolamide resulted in a significant reduction of 72%. In hypercapnic fish, HCO3- fluxes were much higher and perfusion with acetazolamide caused a reduction of HCO3- flux by 38%. The same pattern was observed for fish in recovery, where in all three experimental conditions, there was no significant inhibition of plasma-accessible CA. We also observed no change in CA enzyme activity (measured in vitro) in any of the experimental PCO2 conditions. In summary, our data suggests that there are additional pathways for HCO3- excretion at the gills of hagfish that are independent of plasma-accessible CA.
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Affiliation(s)
- Marina Giacomin
- Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Bldg., Edmonton, AB, T6G 2E9, Canada. .,Bamfield Marine Science Centre, Bamfield, BC, V0R 1B0, Canada.
| | - Jenna M Drummond
- Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Bldg., Edmonton, AB, T6G 2E9, Canada.,Bamfield Marine Science Centre, Bamfield, BC, V0R 1B0, Canada
| | - Claudiu T Supuran
- Neurofarba Department, University of Florence, Via Ugo Schiff 6, Florence, Italy
| | - Greg G Goss
- Department of Biological Sciences, University of Alberta, CW 405, Biological Sciences Bldg., Edmonton, AB, T6G 2E9, Canada.,Bamfield Marine Science Centre, Bamfield, BC, V0R 1B0, Canada
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Clifford AM, Tresguerres M, Goss GG, Wood CM. A novel K + -dependent Na + uptake mechanism during low pH exposure in adult zebrafish (Danio rerio): New tricks for old dogma. Acta Physiol (Oxf) 2022; 234:e13777. [PMID: 34985194 DOI: 10.1111/apha.13777] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Revised: 09/27/2021] [Accepted: 01/01/2022] [Indexed: 12/16/2022]
Abstract
AIM To determine whether Na+ uptake in adult zebrafish (Danio rerio) exposed to acidic water adheres to traditional models reliant on Na+ /H+ Exchangers (NHEs), Na+ channels and Na+ /Cl- Cotransporters (NCCs) or if it occurs through a novel mechanism. METHODS Zebrafish were exposed to control (pH 8.0) or acidic (pH 4.0) water for 0-12 hours during which 22 Na+ uptake ( J Na in ), ammonia excretion, net acidic equivalent flux and net K+ flux ( J H net ) were measured. The involvement of NHEs, Na+ channels, NCCs, K+ -channels and K+ -dependent Na+ /Ca2+ exchangers (NCKXs) was evaluated by exposure to Cl- -free or elevated [K+ ] water, or to pharmacological inhibitors. The presence of NCKXs in gill was examined using RT-PCR. RESULTS J Na in was strongly attenuated by acid exposure, but gradually recovered to control rates. The systematic elimination of each of the traditional models led us to consider K+ as a counter substrate for Na+ uptake during acid exposure. Indeed, elevated environmental [K+ ] inhibited J Na in during acid exposure in a concentration-dependent manner, with near-complete inhibition at 10 mM. Moreover, J H net loss increased approximately fourfold at 8-10 hours of acid exposure which correlated with recovered J Na in in 1:1 fashion, and both J Na in and J H net were sensitive to tetraethylammonium (TEA) during acid exposure. Zebrafish gills expressed mRNA coding for six NCKX isoforms. CONCLUSIONS During acid exposure, zebrafish engage a novel Na+ uptake mechanism that utilizes the outwardly directed K+ gradient as a counter-substrate for Na+ and is sensitive to TEA. NKCXs are promising candidates to mediate this K+ -dependent Na+ uptake, opening new research avenues about Na+ uptake in zebrafish and other acid-tolerant aquatic species.
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Affiliation(s)
- Alexander M. Clifford
- Department of Zoology University of British Columbia Vancouver British Columbia Canada
- Marine Biology Research Division Scripps Institution of Oceanography University of California San Diego La Jolla California USA
| | - Martin Tresguerres
- Marine Biology Research Division Scripps Institution of Oceanography University of California San Diego La Jolla California USA
| | - Greg G. Goss
- Department of Biological Sciences University of Alberta Edmonton Alberta Canada
| | - Chris M. Wood
- Department of Zoology University of British Columbia Vancouver British Columbia Canada
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Allen GJP, Weihrauch D. Exploring the versatility of the perfused crustacean gill as a model for transbranchial transport processes. Comp Biochem Physiol B Biochem Mol Biol 2021; 254:110572. [PMID: 33556621 DOI: 10.1016/j.cbpb.2021.110572] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 01/27/2021] [Accepted: 01/28/2021] [Indexed: 01/01/2023]
Abstract
The study of transbranchial ion and gas transport of water-breathing animals has long been a useful means of modeling transport processes of higher vertebrate organs through comparative physiology. The molecular era of biological research has brought forward valuable information detailing shifts in gene expression related to environmental stress and the sub-cellular localization of transporters; however, purely molecular studies can cause hypothetical transport mechanisms and hypotheses to be accepted without any direct physiological proof. Isolated perfused gill experiments are useful for testing most of these hypotheses and can sometimes be used outright to develop a well-supported working model for transport processes relating to an animal's osmoregulation, acid-base balance, nitrogen excretion, and respiratory gas exchange as well as their sensitivity to pollutants and environmental stress. The technique allows full control of internal hemolymph-like saline as well as the ambient environmental fluid compositions and can measure the electrophysiological properties of the gill as well as the transport rates of ions and gases as they traverse the gill epithelium. Additives such as pharmaceuticals or peptides as well as the exclusion of ions from the media are commonly used to identify the importance of specific transporters to transport mechanisms. The technique can also be used to identify the penetrance, retention, and localization of pollutants within the gill epithelium or to explore the uptake and metabolism of nutrients directly from the ambient environment. While this technique can be applied to virtually any isolatable organ, the anatomy and rigidity of the decapod crustacean gill make it an ideal candidate for most experimental designs.
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Affiliation(s)
| | - Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
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Eom J, Wood CM. Understanding ventilation and oxygen uptake of Pacific hagfish (Eptatretus stoutii), with particular emphasis on responses to ammonia and interactions with other respiratory gases. J Comp Physiol B 2021; 191:255-271. [PMID: 33547930 DOI: 10.1007/s00360-020-01329-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 10/18/2020] [Accepted: 11/15/2020] [Indexed: 11/24/2022]
Abstract
The hagfishes are an ancient and evolutionarily important group, with breathing mechanisms and gills very different from those of other fishes. Hagfish inhale through a single nostril via a velum pump, and exhale through multiple separate gill pouches. We assessed respiratory performance in E. stoutii (31 ppt, 12 ºC, 50-120 g) by measuring total ventilatory flow ([Formula: see text]) at the nostril, velar (respiratory) frequency (fr), and inspired (PIO2) and expired (PEO2) oxygen tensions at all 12 gill pouch exits plus the pharyngo-cutaneous duct (PCD) on the left side, and calculated ventilatory stroke volume (S[Formula: see text]), % O2 utilization, and oxygen consumption (ṀO2). At rest under normoxia, spontaneous changes in [Formula: see text] ranged from apnea to > 400 ml kg-1 min-1, due to variations in both fr and S[Formula: see text]; "normal" [Formula: see text] averaged 137 ml kg-1 min-1, ṀO2 was 718 µmol kg-1 h-1, so the ventilatory convection requirement for O2 was about 11 L mmol-1. Relative to anterior gill pouches, lower PEO2 values (i.e. higher utilization) occurred in the more posterior pouches and PCD. Overall, O2 utilization was 34% and did not change during hyperventilation but increased to > 90% during hypoventilation. Environmental hypoxia (PIO2 ~ 8% air saturation, 1.67 kPa, 13 Torr) caused hyperventilation, but neither acute hyperoxia (PIO2 ~ 275% air saturation, 57.6 kPa, 430 Torr) nor hypercapnia (PICO2 ~ 1% CO2, 1.0 kPa, 7.5 Torr) significantly altered [Formula: see text]. ṀO2 decreased in hypoxia and increased in hyperoxia but did not change in hypercapnia. Acute exposure to high environmental ammonia (HEA, 10 mM NH4HCO3) caused an acute decrease in [Formula: see text], in contrast to the hyperventilation of long-term HEA exposure described in a previous study. The hypoventilatory response to HEA still occurred during hypoxia and hyperoxia, but was blunted during hypercapnia. Under all treatments, ṀO2 increased with increases in [Formula: see text]. Overall, there were lower convection requirements for O2 during hyperoxia, higher requirements during hypoxia and hypercapnia, but unchanged requirements during HEA. We conclude that this "primitive" fish operates a flexible respiratory system with considerable reserve capacity.
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Affiliation(s)
- Junho Eom
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T1Z4, Canada.
| | - Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, BC, V6T1Z4, Canada
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Giacomin M, Dal Pont G, Eom J, Schulte PM, Wood CM. The effects of salinity and hypoxia exposure on oxygen consumption, ventilation, diffusive water exchange and ionoregulation in the Pacific hagfish (Eptatretus stoutii). Comp Biochem Physiol A Mol Integr Physiol 2019; 232:47-59. [PMID: 30878760 DOI: 10.1016/j.cbpa.2019.03.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Revised: 01/30/2019] [Accepted: 03/06/2019] [Indexed: 10/27/2022]
Abstract
Hagfishes (Class: Myxini) are marine jawless craniate fishes that are widely considered to be osmoconformers whose plasma [Na+], [Cl-] and osmolality closely resemble that of sea water, although they have the ability to regulate plasma [Ca2+] and [Mg2+] below seawater levels. We investigated the responses of Pacific hagfish to changes in respiratory and ionoregulatory demands imposed by a 48-h exposure to altered salinity (25 ppt, 30 ppt (control) and 35 ppt) and by an acute hypoxia exposure (30 Torr; 4 kPa). When hagfish were exposed to 25 ppt, oxygen consumption rate (MO2), ammonia excretion rate (Jamm) and unidirectional diffusive water flux rate (JH2O, measured with 3H2O) were all reduced, pointing to an interaction between ionoregulation and gas exchange. At 35 ppt, JH2O was reduced, though MO2 and Jamm did not change. As salinity increased, so did the difference between plasma and external water [Ca2+] and [Mg2+]. Notably, the same pattern was seen for plasma Cl-, which was kept below seawater [Cl-] at all salinities, while plasma [Na+] was regulated well above seawater [Na+], but plasma osmolality matched seawater values. MO2 was reduced by 49% and JH2O by 36% during hypoxia, despite a small elevation in overall ventilation. Our results depart from the "classical" osmorespiratory compromise but are in accord with responses in other hypoxia-tolerant fish; instead of an exacerbation of gill fluxes when gas transfer is upregulated, the opposite happens.
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Affiliation(s)
- Marina Giacomin
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada.
| | - Giorgi Dal Pont
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada; Integrated Group for Aquaculture and Environmental Studies, Department of Animal Science, Federal University of Paraná, Curitiba, Paraná 83035-050, Brazil
| | - Junho Eom
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada.
| | - Patricia M Schulte
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
| | - Chris M Wood
- Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada; Bamfield Marine Sciences Centre, Bamfield, British Columbia V0R 1B0, Canada; Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
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Giacomin M, Eom J, Schulte PM, Wood CM. Acute temperature effects on metabolic rate, ventilation, diffusive water exchange, osmoregulation, and acid–base status in the Pacific hagfish (Eptatretus stoutii). J Comp Physiol B 2018; 189:17-35. [DOI: 10.1007/s00360-018-1191-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 10/30/2018] [Accepted: 11/05/2018] [Indexed: 12/21/2022]
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